This invention relates to loudspeaker systems for producing bass frequencies and more specifically relate to ported speaker systems. This invention falls between open-back cabinets, the Theile-Small aligned ported reflex cabinets, and the transmission line cabinets.
Loudspeaker systems consist of one or more drivers, once known as speakers, in a cabinet. Beginning with A. L. Thuras"" xe2x80x9cSound Translating Devicexe2x80x9d patent in 1930, audio and acoustic engineers have been improving the capabilities of the loudspeaker system with improvements to the speaker cabinet, particularly the vented speaker cabinet. The most notable of these are P. W. Klipsch, R. Ashley, A. N. Thiele, J. E. Benson, R. Small, H. F. Olsen, L. L. Beranek, and R. M. Bullock. These men have studied and refined the original Thuras concept so that highly engineered speaker systems with flat frequency responses can be synthesized easily.
The loudspeaker synthesis design rules are quite strict and depend heavily on an amplifier that has a low output impedance or is highly damped and a speaker (driver) with a low Q and little resonance. Unfortuantely these conditions do not apply to musical instrument amplifiers or speakers. Highly damped amplifiers produce their low output impedance with a significant amount of feedback. While this feedback reduces the output impedance and reduces harmonic distortion, it also tries to overcome power supply limitations. Consequently, the response to being overdriven is substantial, rapidly rising, and high-order harmonics that produce unpleasant listening. Conversely, the present invention works with amplifiers designed to be overdriven. They have little feedback, and consequently, low damping factors. Musical instrument speaker (driver) design values efficiency over low Q and consequently do not have a Q factor as low as the modern high-fidelity drivers.
The transmission line cabinets load the driver, usually the back of the driver, with an acoustic transmission line which is a quarter wave length at the driver""s resonant frequency. L. J. S. Bradbury applied wave theory to earlier observations that fibrous material slowed the speed of sound. Thus, a fiber filled tube could be a shorter, smaller acoustic transmission line. Unfortunately, these lines fail to provide enough damping for the high Q speakers common to the guitar and musical instrument arts.
The Klipsch loudspeaker systems enclose one side of the driver and load the other with a folded horn. This system is not applicable because the folded horn restricts the middle and upper frequency response. Further, according to the Radiotron Designer""s Handbook, edited by F. Langford-Smith, 1957, pages 857 and 858, the volumes of Klipsch systems at about 5,000 cubic inches per driver are larger than the embodiments below.
The functional object of this invention, having the system resonance below the range of interest, is often accomplished with a free-air driver resonance already below the range of interest.
The object of this invention is a speaker system having a driver or drivers in a smaller than prior art cabinet, said cabinet having an air passage, without fiber fill, although might have fiber lining, with a cross-sectional area approximately equal, ranging from xc2xd to {fraction (3/2)}, to the total active area of said driver or drivers, wherein the front sound waves of said drivers exit immediately to the exterior of the cabinet, and wherein said passage receives the rear sound waves of said driver, transmits them to the exterior of the cabinet, and loads the driver or drivers with an acoustic mass that reduces the frequency of driver resonance by more than 20 percent.
To object of this invention is a speaker system having drivers with free-air resonance within the frequency range of interest for said speaker system and having an air passge which loads said drivers to reduce the resonance below the range of interest.
The object of this invention is a speaker system similar to a transmission line type, ie. with approximate constant cross-sectional area per driver, but with a shorter path from the driver or speaker to the exit.
Another object of this invention is a shelter for an electro-mechanical spring reverberation device which partly defines the air passage.
Another object of this invention is a cabinet and speaker combination for a musical instrument which reduces the speaker resonant frequency so that it is below the frequency range of said musical instrument.